1. Field of the Invention
The present invention relates to an electrophotographic system for visualizing an electrostatic latent image on an image carrier with toner particles, transferring the visualized toner image onto a sheet of paper, and fixing the toner image to the sheet with heat or pressure.
2. Description of the Prior Art
Electrophotographic systems now in use mostly employ dry toner as a developer, and are used as copying machines, laser beam printers, or the like. In addition to monochromatic electrophotographic copying machines, there have recently been developed color copying machines based on the electrophotographic principles to meet demands for colored copies in the market.
In the electrophotographic systems, an electrostatic latent image on a photosensitive body with a photosensitive layer is developed into a visual image with toner particles by a developing unit. The developing unit generally has a toner hopper for supplying toner. As the toner is gradually consumed by the developed unit, the amount of toner held by the toner hopper is reduced. Some toner particles tend to stick to the inner wall surface of the toner hopper, producing solidified masses or blocks of toner, or to be deposited in trapping spaces. When toner remains in the toner hopper, the storage capacity of the toner hopper is reduced. Various attempts have heretofore been made to prevent toner from being formed into blocks and reduce the toner particles kept in the trapping spaces, so that the toner contained in the toner hopper can fully be supplied to the developing unit and the storage capacity of the toner hopper can effectively be utilized.
One conventional electrophotographic system as a copying machine is shown in FIG. 15 of the accompanying drawings. The electrophotographic system has an image carrier 1 comprising a belt of synthetic resin such as polyethylene terephthalate coated on its outer surface with a thin photosensitive layer of selenium (Se) or organic photoconductor (OPC). The image carrier 1 is trained around two vertically spaced feed rollers 2, 3 so that the image carrier 1 has a vertically flat surface. The feed rollers 2, 3 are driven to rotate by a drive motor (not shown) to move the image carrier 1 in a circulating manner in the direction indicated by the arrow A. The electrophotographic system also has a developing unit 6 for developing an electrostatic latent image on the image carrier 1 into a visible image with toner particles, the developing unit 6 being disposed closely to the flat surface of the image carrier 1.
The developing unit 6 has a toner hopper 15 for storing a supply of toner 14, a developing roller 84, a doctor blade 30 for limiting the height of toner fibers attached to the developing roller 84, and a plurality of toner feeders 83a, 83b, 83c in the form of wires of the same diameter bent into a rectangular shape and having opposite ends rotatably supported on opposite sides of the toner hopper 15. The toner feeders 83a, 83b, 83c serve to prevent the toner 14 from being formed into blocks or masses, and feed the toner 14 to the developing roller 30.
The conventional electrophotographic system shown in FIG. 15 operates as follows:
In the developing unit 6, the toner feeders 83a, 83b, 83c in the toner hopper 15 rotate in synchronism with the developing roller 84, along circular paths indicated by the dot-and-dash lines at the same speed, for stirring the toner 14 and feeding the toner 14 to the developing roller 84.
When a potential difference is applied between the developing roller 84 and the image carrier 1, the toner 14 fed onto the developing roller 84 is attracted to an electrostatic latent image on the image carrier 1, developing the electrostatic latent image into a visible toner image. As the electrostatic latent image is developed with the toner 14, the toner 14 is consumed by the image development, and the toner 14 in the toner hopper 15 is additionally fed to the developing roller 84 by the toner feeders 83a, 83b, 83c.
As described above, the toner feeders (wires) 83a, 83b, 83c are of the same diameter and rotate at the same speed. Therefore, when the amount of toner 14 supplied to the developing roller 84 by the toner feeder 83a is greater than the amount of toner 14 attracted to the electrostatic latent image on the image carrier 1 by the developing roller 84, since the toner feeders 83b, 83c supply the toner feeder 83a with an amount of toner commensurate with the amount of toner that has been supplied to the developing roller 84 by the toner feeder 83a, the toner on the developing roller 84 tends to be aggregated as the toner is consumed by the developing unit 6.